I like Nadal best of the three (Fed,Djok) as he's the only one of the three who doesn't seem to be a self centered, pretentious #$%&. I would love to claim that he is the best ever (there is an argument) but if he had the additional majors in the prior two AO's, along with the Wimbledon and US Open finals where he gave up fifth set leads there would be no question.
I think Djokovic is the best when rating by all surfaces but Fed was clearly the better on grass. For the record, I think Sampras at his best was better than anyone st their best on grass.
I also believe that if Rafa hadn't had injury issues, neither Federer nor Djokovic would have won a French open.
One thing that cannot be argued is that with multiple titles at each of the four majors, Rafa is clear one of the all time greats.